"Dreamgirls" arrives with more than its share of baggage; the hit Broadway musical, which opened in 1981, is such a cherished icon that it's taken 25 years for it to be made into a movie. But forget "Was it worth the wait?" The burning question is: "Does she do it?"

And the answer is: Yes, "American Idol" finalist Jennifer Hudson takes full possession of the show-stealing character of Effie, nailing her signature number, "And I Am Telling You I'm Not Going." The generously built ingenue who was an also-ran on the hit television amateur hour takes the spotlight with confidence and chops, as a singer and an actress. All, mind you, despite the ghost of Effie Past -- Jennifer Holliday, the role's originator, who is currently raising goose bumps in a YouTube clip of her performance at the 1982 Tony Awards.

But even with Hudson's triumphant arrival and an overall fizzy mood of singing, dancing, pop nostalgia and camp, "Dreamgirls" is an uneven crowd pleaser. With a promising director (Bill Condon, who wrote "Chicago") and a dazzling cast that includes Beyonce Knowles, Jamie Foxx and Eddie Murphy, the movie not only looks good on paper; it looks great on-screen, too. But it also often sags when it should sparkle, lags when it should go lickety-split and plays it safe when, like Effie, it should sell it to the cheap seats.

But it's Christmas. Let's open the presents first. For the uninitiated, "Dreamgirls" takes place in Detroit in the early '60s, when Deena (Knowles), Effie (Hudson) and Lorrell (Anika Noni Rose), calling themselves the Dreamettes, perform in a local amateur competition. They don't win, but they catch the eye of a car salesman named Curtis Taylor Jr. (Foxx), who has a nose for music and the hustle to make it pay. Taylor -- a vague analogue to Motown founder Berry Gordy -- becomes the group's manager and producer and embarks on a romance with the zaftig Effie, whose angelic voice belies the street-smart fighter underneath.

In time, and against the backdrop of segregation and the burgeoning civil rights movement, Taylor sees crossover potential in the Dreamettes and, catering to the all-powerful visual medium of television and the tastes of white audiences, decides to do a little tweaking. He changes the group's name to the Dreams and instead of putting their strongest singer, Effie, out front, he casts the more conventionally beautiful Deena as the leader. This doesn't sit well with Effie, and she becomes more cantankerous until she is finally drummed out of the act. And I am telling you . . . Well, let's just say, cue showstopper No. 1.

As the aggrieved Effie, Hudson gives that iconic song every bit of the melodrama and fire that make it a diva-worthy aria. (She does the same thing later with the similarly rousing "I Am Changing," a performance that recalls a young Aretha Franklin.) But aside from one or two other notable songs, "Dreamgirls" is devoid of tunes that are memorable from a lyrical or musical point of view. Indeed, for a show about soul music, much of the fare sounds like a musical-theater version of soul, as white-bread as the satirical pop version of Taylor's first hit as a producer, "Cadillac Car."

If the first lump of coal in the "Dreamgirls" stocking is the music, the others have to do with direction and the structure of the show itself. Condon seems to go from zero to 60 throughout the film, overediting wildly in the opening sequence and then letting starchy, expository scenes play on and on. (A montage featuring Knowles in myriad wigs and campy costumes and set to the awful song "When I First Saw You" drives home an already well-established point: She's Diana Ross! We get it! Move on!)

Because of the way "Dreamgirls" is constructed -- Effie is the real star -- the film's biggest names, Knowles and Foxx, are largely wasted. Foxx, whose impersonation of Ray Charles in "Ray" earned him an Oscar, winds up especially empty-handed here, bereft of any good songs or electrifying moments. Luckily Knowles -- who graciously cedes center stage for much of the film -- gets her due in the film's final 10 minutes, when she triumphantly belts out the terrific new song "Listen" (cue showstopper No. 3).

But enough coal. Let's talk about the best part of "Dreamgirls," which isn't the lavish production numbers or the over-the-top costumes or even the contagious excitement of a gifted young singer making her Streisand-like debut. Let's talk about Eddie Murphy, who jump-starts every scene he's in as James "Thunder" Early, a Little Richardesque R&B singer whose career so starkly represents the costs of crossover success. Once again proving that he's a singer, actor and comedian to contend with, Murphy steals scenes even from the show's designated scene-stealer. "Dreamgirls" fans will no doubt come for Effie, but they may find themselves staying for Eddie.

Dreamgirls (131 minutes, at area theaters) is rated PG-13 for profanity, some sexuality and drug use.